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  • E 128 cfi/Ber. DKG 89 (2012) No. 5

    Process Engineering

    Introduction For new developments of kilns for sanitaryware all plant components are to be submitted to thorough examinations in view of their design and construction as well as the required process and materials tech- nology to find possible modifications which allow the plant to perfectly fulfill their function. The focal points in this connection are energy saving

    and the associated reduction of CO2 emissions, including considering the appropriate heating methods and transport methods, design of heat insulating and heat absorbing com- ponents. The latest methods for determining stationary and transient heat transmission processes and for simulating flows for the optimisation of heat transmission and tempera- ture uniformity, e.g. via computer calculations, are used for this pur- pose. The respective requirements are listed in a specification bringing out solutions such as the Energy Management System (EMS), Com- bined Heat Supply Network and the completely redesigned Riedhammer REKO shuttle kiln. The effectiveness of these newly developed products is documented by the respective oper- ational data.

    Initial situation The production of ceramic products is always closely linked with thermal processes. As ceramic sanitaryware is fired at relatively high temperatures between 1180 °C and 1250 °C the theoretical energy requirement for obtaining such temperatures and without consideration of different heats of transition already amounts to 295–320 kcal/kg. The diverse products with their different weights require kiln furniture as refractory supports during firing which are

    used in a weight ratio of ware : kiln furniture = 1 : 1,1 to 1 : 1,3 [1]. This leads to a more than doubled mass of ceramic products to be fired and the theoretical energy requirement increases accordingly. Whereas only a small quantity of energy consuming transport means are used in roller kilns as no kiln cars are necessary in this kiln type – (taking into account the slightly increased radiation losses of the transport rollers at the outer kiln wall) – the cars with their refractory superstructure have to be consid- ered for the energy calculation in shuttle and tunnel kilns with car transport systems (Fig. 1). In these kiln types the heating is effected according to the laws of transient heat conduction. With modern com- puter simulation calculation meth- ods [2] the most favourable change in enthalpy can be determined as a function of the firing cycle and of the temperature dependent on the refractory car insulation to be select- ed. On average the roller kilns have an approx. 25 % lower energy con- sumption in comparison with tunnel kilns with car conveyance. Riedhammer has always focused on obtaining the lowest possible energy consumption for its kiln plants. According to Tab. 1 which draws a comparison between standard tun- nel kilns with car transport and standard tunnel kilns available on the world market, up to 55 % of the energy costs and, due to the phys- ical connection, also the corres- ponding amount of CO2 emissions can be saved by using the available technology and experience. For this comparison a production capacity of 50 t/d and a natural gas price of EUR 0,3/m³n were taken as a basis. With up to 103 % the differences between Riedhammer roller kilns and conventional tunnel kilns are even more significant which is repre- sented in Tab. 2. The same fuel prices as for Tab.1 were taken as a calculation basis, assuming, howev- er, production capacities of 30 t/d. All kiln types for the sanitary ceram- ic industry are fossil fuel heated. The enormous capacities – more than 50 t/d are no rarity – require large plant cross sections [3] for which

    Riedhammer/Sacmi Kilns – Latest Developments for Sanitaryware

    Jörg Ridder, David Lindl Riedhammer GmbH 90411 Nürnberg, Germany E-mail: joerg.ridder@riedhammer.de www.riedhammer.de

    Fig. 1 Tunnel kiln with kiln car conveyance for firing sanitaryware

    Tab. 1 Comparison of energy and emission data of tunnel kilns

    Riedhammer Tunnel Kiln Standard

    Tunnel Kilns Available on the Market

    Energy consumption [kcal/kg net]

    814 1260

    Energy consumption [kcal/kg charge]

    387 599

    Total fuel costs [EUR/a] 519 767 802 326

    Total CO2 emission [kg/a] 3 465 116 5 348 837

    Difference +55 %

  • electrical heating is not suitable for structural and thermo-technical rea- sons. Due to the inevitable waste gas loss- es the degree of efficiency in fossil fuel heated kiln plant is lower than in case of electrical heating, but the high prices for electric energy in most countries not only neutralise the efficiency advantage but also speak in favour of fossil fuel heating in view of the operating costs. It does not appear that electric en- ergy generated by renewable en- ergies will be obtainable at lower prices than fossil-fuel energy in the foreseeable future. In the ceramic sanitaryware industry light heating oil and fuel gases are used as fossil fuels; the use of heavy oil is very rare. For the transport through the pipes to the burner and for combustion purposes the heavy oil must be brought to a specific and constant viscosity which can only be realised with considerable effort and costs by means of piping with con- trolled heating. Components in the heavy oil, such as sulphur, react with the glaze and lead to higher reject rates. The use of coal dust as fuel

    would contaminate the sanitaryware products even more so that this type of fuel is to be regarded as inappro- priate. In the vast majority of the cases nat- ural gas is used as fuel in the ceram- ic sanitaryware industry. In Central Europe the natural gas prices are mostly bound to the price development of light and heavy heating oil due to long-term supply contracts of the natural gas im- porters with the suppliers of the sup- plying countries. Therefore the price index for natural gas follows that for heating oil with a small time delay. However, the upward trend of the import prices over the last decade (Fig. 2) [4] is to be regarded as an unpleasant common tendency. Due to the shortage of resources this trend is most likely to intensify in the future. The import prices for natural gas are indicated on the left coord- inate in EUR t/a, the prices for crude oil in EUR t/a are shown on the right coordinate. The most significant price increases took place in the years 2000 to 2001 and 2004 to 2008, the prices in the year 2009 were only on the decline due to the

    worldwide economic crisis. The ten- dencies shown remain unchanged also in the case of an inflation-adjust- ed consideration. Every combustion process of carbon dioxide and hydrocarbons causes the formation of nitrous oxides and above all of carbon dioxide gases. The thermal NOx formed during combustion mainly consists of NO and 5 % of NO2 These nitrogen compounds act as acid formers in the presence of water and therefore cause the so-called “acid rain“ in the atmosphere. The reduction of NOx during combustion is achieved by well-known primary and secondary measures, as described in the rele- vant literature [5]. The CO2 gas which is also referred to as ”greenhouse gas“ is a synonym for harmful impacts on the environ- ment. It heats up the air at ground level by absorbing the infrared radi- ation of the earth’s crust and cools down the higher spheres by radi- ation. The CO2 emission is directly related to the fuel consumption. Low per- cent values in the waste gas are not an indication for a low CO2 emission

    Process Engineering

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    Best Results for Minerals, Refractories, Ceramics and Geology

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    • From Mine to Concentrates to Final Products

    • For Research and Industrial Applications

    www.bruker.com/x-ray

  • cation for new development of kiln plants: • Kilns are to be heated with fossil

    fuels for reasons of costs and oper- ational safety.

    • Despite intensive efforts in view of the composition of the materials the high firing temperature will not change considerably in the future.

    • The mass ratio of the kiln furniture to product can be improved by using SiC materials.

    • The lowest possible energy con- sumption can be achieved in roller kilns due to low ballast and/or kiln furniture quantities.

    • Modern computer-assisted calcu- lation methods permit the ener- getic optimisation of the transport car insulation.

    • The CO2 emissions are to be reduced.

    • The energy consumption is to be minimised significantly.

    The requirements indicated led to the following new developments by Riedhammer: • Energy Management System

    (EMS) for all continuously oper- ated firing kilns

    • Combined Heat Supply Network between the firing units and the consumers in the factory

    • REKO shuttle kiln. These new developments are the result of Riedhammer’s experience from more than 88 years in the con- struction of kilns for the ceramic industry and the in-house synergy effects of the new technical kiln developments for sanitary and table - ware ceramics, for advanced ceram- ics, refractories and carbon. It remains the company’s central task to continue with the design and construction of kilns with the mini- mum possible energy consumption

    and CO2 emission

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